Investigating and calibration methods on signal quantification for Magnetic Particle Imaging (MPI)

Abstract

Magnetic Particle Imaging (MPI) is an emerging imaging modality that enables the quantitative and real-time visualization of superparamagnetic iron oxide nanoparticles (SPIONs). Its unique ability to directly detect and quantify SPION concentrations in vivo has positioned MPI as a promising tool for various biomedical applications, including cancer detection, targeted drug delivery, and cell tracking.^1,2 However, achieving accurate and reproducible quantification requires standardized calibration approaches that account for differences in SPION properties and experimental conditions.^3-5

Herin we examine systematic differences in signal quantification of two calibration methods employing two commercially available tracers employed in MPI: ProMag and VivoTrax. The methods were: a fixed-volume approach, commonly used in biological studies for dilution series and calibration curves; and a fixed-concentration approach, which maintains a constant SPION concentration while increasing total iron content. Analysis revealed significant differences in signal quantification between the two calibration methods, with more pronounced discrepancies observed as dilution increased. These differences were likely due to reduced SPION-SPION interactions at lower concentrations, leading to reduced signal strength and broader (lower resolution) images. These findings highlight the potential advantages of the fixed-concentration method, which helps preserve SPION-SPION interactions and may offer improved accuracy, particularly when maintaining stable nanoparticle interactions is crucial.

This study highlights the importance of SPION properties, environmental interactions, and calibration methods in MPI signal quantification. Differences in SPION behaviour, especially at varying concentrations, affect the MPI signal. By comparing calibration methods, this work aims to standardize MPI protocols, ensuring more accurate results in solution-based experiments and providing a foundation for future cell-based studies. The findings enhance understanding of MPI signal behaviour under various calibration methods, enabling more precise SPION quantification.